<template>
  <scroll
          :data="data"
          class="listview"
          ref="listview"
          :listenScroll="listenScroll"
          @scroll="scroll"
          :probeType="probeType"
          >
    <ul>
      <li v-for="(group,indexs) in data" class="list-group" ref="listGroup" :key="indexs">
        <h2 class="list-group-title">{{group.title}}</h2>
        <uL>
          <li @click="selectItem(item)"  v-for="(item,index) in group.items" class="list-group-item" :key="index" >
            <img class="avatar" v-lazy="item.avatar">
            <span class="name">{{item.name}}</span>
          </li>
        </uL>
      </li>
    </ul>
    <div class="list-shortcut"  @touchstart="onShortcutTouchStart"  @touchmove="onShortcutTouchMove">
      <ul>
        <li v-for="(item, index) in shortcutList" :data-index="index" class="item"  :key="index" :class="{'current': currentIndex == index}" >{{item}} 
        </li>
      </ul>
    </div>
    <div class="list-fixed" ref="fixed" >
      <div class="fixed-title">{{ fixedTitle }} </div>
    </div>
    <div v-show="!data.length" class="loading-container">
      <loading></loading>
    </div>
  </scroll>
</template>

<script type="text/ecmascript-6">
  import Scroll from 'base/scroll/scroll'
  import Loading from 'base/loading/loading'
  import {getData} from 'common/js/dom'
    
    //  一个锚点的高度是18
  const TITLE_HEIGHT = 30
  const ANCHOR_HEIGHT = 18

  export default {
    data(){
        return{
            scrollY : -1,
            currentIndex : 0,
            diff: -1
        }
    },
    props: {
      data: {
        type: Array,
        default: []
      }
    },
    computed: {
      shortcutList() {
        return this.data.map((group) => {
          return group.title.substr(0, 1)
        })
      },
      fixedTitle() {
        if (this.scrollY > 0) {
          return ''
        }
        return this.data[this.currentIndex] ? this.data[this.currentIndex].title : ''
      }
    },
    created() {
        this.touch = {};
        this.listenScroll = true;
        this.probeType = 3;
        this.listHeight = [];
    },
    methods: {
    
        selectItem(item) {
             this.$emit('select', item)
        },
        onShortcutTouchStart(e) {
            let anchorIndex = getData(e.target, 'index')
            // 看看第一次点击的锚点是第几个
            this.touch.anchorIndex = anchorIndex;
            this.scrollTo(anchorIndex);
            let firstTouch = e.touches[0];
            this.touch.y1 = firstTouch.pageY;;
        },

        onShortcutTouchMove(e){
            let firstTouch = e.touches[0];
            this.touch.y2 = firstTouch.pageY;
            // 获取按住拖动的时候经过了几个锚点 , | 0 相当于Math.floor();
            let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0;
            // 再加上之前的锚点个数
            let anchorIndex = Number(this.touch.anchorIndex) + delta;
             this.scrollTo(anchorIndex);
            // console.log(delta);
        },
        scroll(pos){
            this.scrollY = pos.y;
        },
        _calculateHeight(){
                 this.listHeight = []
            const list = this.$refs.listGroup
            let height = 0
            this.listHeight.push(height)
            for (let i = 0; i < list.length; i++) {
                let item = list[i]
                height += item.clientHeight
                this.listHeight.push(height)
            }
        },
        refresh() {
            this.$refs.listview.refresh()
        },
        scrollTo(index){
            if (!index && index !== 0) {
                return
            }
            if (index < 0) {
                index = 0
            } else if (index > this.listHeight.length - 2) {
                index = this.listHeight.length - 2
            }
            this.scrollY = -this.listHeight[index]
            // console.log(this.scrollY);
            // this.currentIndex = index;
            this.$refs.listview.scrollToElement(this.$refs.listGroup[index],0);
        },
      
    },
    watch: {
        data(){
            setTimeout(() => {
                this._calculateHeight();
            }, 20);
        },
        scrollY(newY){
            const listHeight = this.listHeight
            // 当滚动到顶部，newY>0
            if (newY > 0) {
                this.currentIndex = 0
                return
            }
            // 在中间部分滚动
            for (let i = 0; i < listHeight.length - 1; i++) {
                let height1 = listHeight[i]
                let height2 = listHeight[i + 1]
                if (-newY >= height1 && -newY < height2) {
                    this.currentIndex = i
                    this.diff = height2 + newY
                    return
                }
            }
            // 当滚动到底部，且-newY大于最后一个元素的上限
            this.currentIndex = listHeight.length - 2
        },
        diff(newVal) {
            let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
            if (this.fixedTop === fixedTop) {
            return
            }
            this.fixedTop = fixedTop
            this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
        }
    },
    components: {
      Scroll,
      Loading
    }
  }

</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
  @import "~common/stylus/variable"

  .listview
    position: relative
    width: 100%
    height: 100%
    overflow: hidden
    background: $color-background
    .list-group
      padding-bottom: 30px
      .list-group-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
      .list-group-item
        display: flex
        align-items: center
        padding: 20px 0 0 30px
        .avatar
          width: 50px
          height: 50px
          border-radius: 50%
        .name
          margin-left: 20px
          color: $color-text-l
          font-size: $font-size-medium
    .list-shortcut
      position: absolute
      z-index: 30
      right: 0
      top: 50%
      transform: translateY(-50%)
      width: 20px
      padding: 20px 0
      border-radius: 10px
      text-align: center
      background: $color-background-d
      font-family: Helvetica
      .item
        padding: 3px
        line-height: 1
        color: $color-text-l
        font-size: $font-size-small
        &.current
          color: $color-theme
    .list-fixed
      position: absolute
      top: 0
      left: 0
      width: 100%
      .fixed-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
    .loading-container
      position: absolute
      width: 100%
      top: 50%
      transform: translateY(-50%)
</style>
